In the digital communications field, there is a vast application demand for speech, image, audio, and video transmission, such as mobile phone communication, audio and video conference, broadcast television, and multimedia entertainment. A speech/audio signal is digitized and transferred from one terminal to another terminal by using a communications network. The terminal herein may be a mobile phone, a digital telephone terminal, or a speech and audio terminal of any other type. The digital phone terminal may be, for example, a VOIP telephone, an ISDN telephone, a computer, or a cable communications telephone. To reduce resources occupied in a storage or transmission process of a speech/audio signal, the speech/audio signal is compressed at a transmit end and is transmitted to a receive end, and the receive end restores the speech/audio signal by decompressing processing and plays the speech/audio signal.
In an actual speech communication process, bandwidth of a speech/audio signal often changes. A cause that leads to the bandwidth change of the speech/audio signal may be a change of a network status, may be a bandwidth change of the speech/audio signal itself, or may be another factor that can cause switching of the speech/audio signal between a high-frequency signal and a low-frequency signal. The process in which a speech/audio signal switches between high and low frequencies is referred to as wideband switching.
Specifically, the network status often changes and network bandwidth becomes narrow as the network status deteriorates. Accordingly, with the change of the network bandwidth, the speech/audio signal also needs to switch between the high-frequency signal and the low-frequency signal. When the network bandwidth becomes narrow, the speech/audio signal needs to change from the high-frequency signal to the low-frequency signal; when a network situation recovers, the speech/audio signal needs to recover from the low-frequency signal to the high-frequency signal. A bandwidth size of the high-frequency signal and the low-frequency signal is a relative concept. For example, bandwidth of the high-frequency signal is 0-16 kHZ and bandwidth of the low-frequency signal is 0-8 kHz; or bandwidth of the high-frequency signal is 0-8 kHz and bandwidth of the low-frequency signal is 0-4 kHz, where the high-frequency signal is also an ultra-wideband signal and the low-frequency signal is also a wideband signal.
However, after wideband switching is performed by using the prior art at an encoder, a problem of discontinuous speech/audio signals often occurs at a decoder, which thereby degrades speech communication service quality.